Chlorofluorocarbons (CFCs), e.g., chlorotrifluoromethane and dichlorodifluoromethane, and hydrochlorofluorocarbons (HCFCs), e.g., chlorodifluoromethane, have conventionally been used as working media for heat cycling, such as, for example, working media for refrigerators, working media for air conditioners, wording media for electric-power generation systems (e.g., waste heat recovery power generation), working media for latent-heat transfer devices (e.g., heat pipes), and secondary refrigerants. However, it is pointed out that such CFC and HCFC affect the ozone layer of the stratosphere, and use of these compounds is restricted at present.
Under these circumstances, hydrofluorocarbons (HFCs) which less affect the ozone layer, such as difluoromethane (HFC-32), tetrafluoroethane, and pentafluoroethane (HFC-125), have come to be used as working media for heat cycling in place of the CFCs or HCFCs. For example, R410A (pseudoazeotropic-mixture working medium composed of HFC-32 and HFC-125 in a mass ratio of 1:1) is a working medium which is widely used. However, it is pointed out that HFC may be a cause of global warming.
R410A is widely used in common air conditioners including the so-called packaged air conditioners and air conditioners for domestic use because of the high refrigerating capacity thereof. However, R410A has a global warming potential (GWP) as high as 2088, and it is desired to develop a low-GWP working medium.
Recently, hydrofluoroolefins (HFOs), i.e., HFC having a carbon-carbon double bond, have come to be attracting attention as a promising working medium which less affects the ozone layer and less affects the global warming, because the carbon-carbon double bonds thereof are apt to be cleaved by OH radicals present in the air. In this description, a saturated HFC is referred to as HFC and distinguished from an HFO, unless otherwise indicated. There are cases where an HFC is referred to as a “saturated hydrofluorocarbon”. Although halogenated hydrocarbons such as HFC and HFO are each indicated by the compound name accompanied by an abbreviation thereof in parentheses, abbreviations only are often used in place of the compound names in this description according to need.
With respect to a working medium including an HFO, Patent Document 1, for example, discloses a technique concerning a working medium including 1,1,2-trifluoroethylene (HFO-1123), which has those properties and brings about excellent cycle performance. Patent Document 1 indicates that for the purpose of enhancing the noncombustibility, cycle performance, etc. of that working medium, it was attempted to use HFO-1123 in combination with any of various HFC to obtain a working medium.
It is known that in cases when HFO-1123 is used alone, the HFO-1123 decomposes by itself at a high temperature or a high pressure if there is an ignition source. There is a report in Non-Patent Document 1 that an attempt was made to inhibit the self-decomposition reaction by mixing HFO-1123 with another ingredient, e.g., vinylidene fluoride, to obtain a mixture having a reduced HFO-1123 content.
Patent Document 2 proposes to use HFO-1123 alone as a working medium in heat cycle systems and to use a mixture of HFO-1123 with HFC-32 or a mixture of HFO-1123 with HFO-1234yf as a working medium.